Kobelco 20-Ton 8-Series Excavator Main Control Valve (MCV) Spool Functions Guide
Overview: The Main Control Valve (MCV) is the hydraulic core of the Kobelco 20-ton 8-series excavator, directing hydraulic fluid from pumps to actuators. This comprehensive bilingual guide details the positions and operational functions of the 12 primary spools and auxiliary valves within the MCV block.
1. Main Control Valve (MCV) 12 Spool Functions
The Kobelco 20-ton excavator MCV houses 12 individual spools that govern specific hydraulic circuits [cite: 19]. Below is the complete functional breakdown:
| Spool Name | Function / Description |
|---|---|
| P1 Unloading Spool | 1. Cools unused hydraulic oil from the P1 side and returns it to the hydraulic tank. 2. In neutral state (engine running, safety lock lever not lowered), P1-side oil returns directly to the tank. |
| Right Travel Spool | Controls the right travel motor to achieve right-side travel. |
| Boom Spool | Controls boom raise and lower operations. |
| Bucket Spool | Controls bucket curl and dump actions. |
| Arm Spool 2 | Regeneration (combine-flow) spool — increases arm-curl speed. |
| Left Travel Spool | Controls the left travel motor to achieve left-side travel. |
| Boom Combine Spool | Boom-raise combine flow — increases boom-up speed. |
| Swing Spool | Controls the swing motor for machine rotation. |
| Arm Spool 1 | Basic control of arm extend and curl. |
| Optional Attachment Spool | Reserved / standby spool; activated when adding attachments such as a breaker or hydraulic shear. |
| P2 Unloading Spool | 1. Cools unused hydraulic oil from the P2 side and returns it to the hydraulic tank [cite: 19]. 2. In neutral state (engine running, safety lock lever not lowered), P2-side oil returns to tank. |
| Travel Straight Spool | During combined operations (swing/boom + travel), keeps travel straight and prevents drifting. |
2. Auxiliary Valve Functions in the MCV Block
In addition to the main spools, the MCV incorporates several specialized auxiliary valves to maintain hydraulic stability, prevent backflow, and regulate pressures.
| Valve Name | Function / Description |
|---|---|
| Lift Valve | Stabilizes the oil circuit and prevents vibration. |
| Check Valve | Prevents reverse flow of hydraulic oil. |
| Pressure Reducing Valve | Reduces pressure in a local circuit of the hydraulic system, providing the excavator with stable pressure lower than the supply pressure from the hydraulic pump. |
| Bypass Cutoff Valve | Controls hydraulic oil flowing from each central bypass circuit to the low-pressure passage. |
| Hold Valve | Reduces leakage based on the holding pressure from each cylinder. |
| Boost Check Valve | Generates boosted pressure required for the low-pressure passage. |
